1. Field of the Invention
The invention relates to a novel process for preparing triaryl-s-triazines from aromatic nitriles, and triaryl-s-triazine ring containing or cross-linked polymers or copolymers from aromatic nitrile-modified (terminated and/or appended) prepolymers or precopolymers in the presence of a novel catalyst and relates to the novel compounds and polymers produced by the above process. More particularly, the invention relates to the use of the novel process, polymers and compounds to produce fiber-reinforced composites of outstanding thermal-oxidative stability.
2. Description of the Prior Art
Conventional condensation-type aromatic polyimides, polybenzimidazoles, polvimidazopyrrolones, and polyquinoxalines exhibit excellent thermal-oxidative stability, but they are, however, difficult to process into fiber-reinforced composites. Various workers have attempted to solve the processability problem of these high temperature resistant polymers with varying degrees of success.
Prior to the present invention, aromatic nitriles were trimerized at a temperature in the range of 350.degree. C. to 500.degree. C. and under a pressure of 35,000 to 50,000 atmospheres. Bengelsdorf, I. S., "High Pressure High Temperature Reactions. I. The Trimerization of Aromatic Nitriles", J. Amer. Chem. Soc., Vol. 80, p. 803 (1958). In U.S. Pat. No. 2,503,999, Cairns et al. trimerized aromatic nitriles at a temperature in the range of 60.degree. C. to 150.degree. C. and under a pressure above 3,000 atmospheres with an alcohol catalyst. In U.S. Pat. No. 1,989,042, Kunz et al. trimerized aromatic nitriles below room temperature with chlorosulfonic acid served as both the solvent and catalyst. In U.S. Pat. No. 2,598,811, Mahan et al. trimerized aromatic nitriles at a temperature in the range of 66.degree. C. to 288.degree. C. and under a pressure in the range of 30 p.s.i. to 500 p.s.i. with a catalyst selected from the groups consisting of hydrides and amides of alkali metals, and hydrides of alkaline earth metals. In U.S. Pat. No. 3,095,414, Spainhour synthesized triazines at a temperature in the range of 25.degree. C. to 150.degree. C. in a sealed reactor with a catalyst mixture selected from one group consisting of metallic salts such as titanium tetrachloride and another group consisting of organometallic compounds such as trialkyl aluminum. In U.S. Pat. No. 3,060,179, Toland polymerized aromatic nitriles at a temperature in the range of 200.degree. C. to 400.degree. C. in an open or pressure vessel with a metal salt catalyst selected from the group consisting of copper, manganese, and cobalt. In U.S. Pat. No. 3,678,049, Gump polymerized aromatic nitriles at a temperature in the range of 200.degree. C. to 350.degree. C. in an autoclave under an initial pressure of about 0.001 mm of Hg with 2-pyrrolidinone served as both the catalyst and solvent. Because of either the superhigh pressure required or the quantity and particularly the nature of catalyst used, none of the trimerization methods previously described are suitable for processing the aromatic nitrile-modified (terminated and/or appended) condensation type prepolymers into a s-triazine ring cross-linked high temperature resistant matrix resins for fiber reinforced composites.
Prior to the present invention, Lubowitz, in U.S. Pat. No. 3,528,950, developed a new system of processable thermally stable modified polyimides as matrices for fiber-reinforced composites. These processable modified polyimides, known as addition-type polyimides were made from imide oligomers terminated with norbornene groups. After removal of the solvent, these norbornene-terminated imide oligomers can be polymerized and/or cross-linked by an addition reaction primarily through the double bonds to yield thermally stable polyimides without the evolution of by-products. Fiber-reinforced composites made from these norbernene-terminated polyimides, however, cannot reach an upper service temperature of about 315.degree. C. This is apparently due to the presence of the aliphatic cyclic structure derived from the norbornene groups.